Start the inbound receiver

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With annotations already indicating idempotentHint and non-read-only, the description adds substantial context: it explains that under HTTP the receiver is already mounted and only reports the address, while on stdio it binds a listener. It also warns about reachability from the participant and recommends setting RECEIVER_PUBLIC_URL for remote cases, which goes beyond any annotation.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is slightly long but every sentence adds value: setup purpose, ordering, transport-specific behavior, idempotency, and remote configuration. It is well-structured front-loaded with the core purpose and then expands into necessary details without redundancy.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the simple schema (one optional param) and presence of an output schema, the description fully covers necessary context: when to call, transport differences, idempotency, and remote reachability. It also mentions the output ('report the URL') even though an output schema exists, so the agent is well-equipped.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema covers the sole parameter session_id with 100% coverage, including its behavior ('Include a session to get its exact callback URL back. Omit for just the base URL.'). The description itself does not add further parameter-specific meaning, so the baseline of 3 applies without needing compensation.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose with a specific verb and resource: 'Make sure this mock can receive the participant's callbacks, and report the URL it must use.' It distinguishes from siblings like receiver_stop and session_create by emphasizing its role as an initialization step ('Call it once before session_create').

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides explicit usage timing: 'Call it once before session_create.' It also gives context about transport differences and remote participant configuration. However, it does not explicitly state when not to use the tool or compare it directly with alternatives like receiver_stop, so it lacks full when/when-not/alternatives coverage.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.